This invention relates to correcting angular bone deformities, and more particularly to an orthopedic device and method for correcting angular deformities of the lower extremities, such as genu varus and genu valgus conditions.
Angular bone deformities of the lower extremities are typically characterized by abnormal angulations of the lower leg in relation to the thigh. For example, genu varum is characterized by an abnormal outward bowing of the leg resulting in bowlegs, while genu valgum is characterized by an inward bowing of the leg and is commonly referred to as knock-knees. Under normal conditions, the femur and tibia meet at a tibial-femoral angle of approximately 5-12 degrees of valgus. A greater angle results in a genu valgus condition while a lesser angle results in a genu varum condition. Either of these conditions in one or both legs may result in improper load distribution on the knee joint, causing swelling, knee pain, loss of stability, subluxation, increased joint arthritis, and other conditions that restrict one's lifestyle.
Angular bone deformities in young children can be caused by the following conditions, which are by no means exhaustive: Blount disease, Cerebral Palsy, Larsen's Syndrome, dysplastic disorders, rickets, chronic inflammatory arthritis, neuromuscular causes of hypotonia and fractures.
Various procedures have been developed for treating genu varum and genu valgum in young patients, such as children and adolescents that have not reached full growth. One such procedure is known as cuneiform or wedge osteotomy in which a wedge-shaped section of bone is surgically removed to allow realignment of the bone. The wedge cut made by the surgeon should not completely sever the tibia so that a bridge of residual bone is intact to effectually serve as a hinge for reduction of the wedge-shaped gap that remains following removal of the bone wedge. The depth of the wedge is critical in that if the wedge is too shallow, thus rendering the bridge too wide, the resulting wide fulcrum results in over stressing of the medial cortex during wedge compression, causing fracture of the bone bridge. If the wedge is too deep (the residual bone bridge is too narrow) the residual bone bridge, if not completely severed, may lack sufficient strength to provide medial stability to the reduced osteotomy. Reduction of the wedge-shaped gap allows realignment of the bone, and correction of the loading patterns of the leg. Bone plates are then installed to secure the reshaped bone, at least through the healing process. Although this technique has proven widely successful for adults that have no other recourse or for severe deformities that cannot be corrected by any other means, it is preferable to use less invasive procedures for children and adolescents that have not reached their full stature.
One less invasive procedure for treating the valgus and varus conditions of children or adolescents still in the growth stage includes damaging or destroying one half of the physis or growth plate of the distal femur or proximal tibia by scraping or cutting, with the premise that the undamaged portion will continue to grow in an asymmetric manner to affect the angulation of the lower extremity. However, this technique involves destruction of one half of the growth plate and therefore not a viable option for all patients.
Another less invasive procedure is known as hemiepiphyseal stapling. The principal steps of this procedure are as shown in FIGS. 1A-1C. For a genu valgus condition, a staple 10 is driven into the lateral side 15 of the distal femur 12 about the distal femur physis or growth plate 18. For a genu varus condition, the staple 10 would alternatively be driven into the medial side 22 of the distal femur 12 about the growth plate 18. Other locations for stapling may include the lateral or medial sides of the proximal tibia 24. The staple 10 has two prongs 14, 16 that straddle the distal femur growth plate 18 and a cross member 20 that extends between the prongs 14, 16. Typically, the prongs are oriented perpendicular to the cross member 20. Depending on the age and amount of angular deformity, more than one staple may be used. Ideally, the staple 10 with its prongs 14, 16 promote asymmetric growth on the medial side of the growth plate 18, while inhibiting growth on the lateral side of the growth plate 18 as shown by growth lines 26 and growth distance 28 in FIG. 1B, to thereby reduce the initial tibial-femoral angle a1 (FIG. 1A) to a more acceptable angle a2 (FIG. 1B)
Although hemiepiphyseal stapling is, in some instances, advantageous over other techniques, it suffers from numerous drawbacks. For optimal bone angle correction, growth of the physis should be inhibited on one and unrestricted on the opposite side. However, since the staple 10 must have prongs 14, 16 of sufficient length to ensure firm anchorage into the distal femur, more of the physis may be restricted from growth than desired, leading to less bone angle correction. By way of example, if the prongs extend approximately ⅓ distance into the bone, than approximately ⅓ of the physis will be restricted from growth due to prong resistance. If the stapling procedure is performed toward the end of the growth cycle (13-15 years of age for girls and 16-17 years of age for boys) and does not produce the desired results, then more invasive procedures, such as wedge osteotomy as described above, may have to be performed.
In addition, the staple itself must be inserted with extreme caution, and always in conjunction with radiography to ensure that the ends of the prongs are sufficiently spaced from the growth plate to prevent its damage. Moreover, the dense fibrous tissue (known as the perichrondial ring of LaCroix) that surrounds, anchors and supports the physis during the growth phase may become permanently damaged by the cross member 20 if the staple 10 is inserted too far into the bone.
It would therefore be desirous to provide an orthopedic implant and method for correcting angular bone deformity which minimizes or eliminates the deficiencies of the prior art devices and techniques. It would be further desirous to provide the orthopedic implant and method which promotes asymmetric growth of the growth plate without damaging fibrous tissue by means of a pivotal motion of one part of the device relative to another.